Low-temperature heater for heating air



Nov. 7, 1950 P. G. VICARD Q 2,528,523

LOW-TEMPERATURE HEATER FOR HEATING AIR Filed.July 10, 1947 ummnmuuuunmmmmm llllllllllllllllll Patented Nov. 7, 1950 OFFICE LOW-TEMPERATUREHEATER FOR HEATING AIR Pierre Georges Vicard, Lyon, France ApplicationJuly 10, 1947, Serial No. 760,056

. In France April 11, 1941 Section 1, Public Law 690, August 8, 1946Patent expires April 11, 1961 4 Claims.

The present invention relates to low temperature heaters and has amongits objects the provisions of simple construction and particularlyeconomical utilization of the heat developed in the combustion chamberof such heaters.

The improvement essentially consists in arranging the flow of thecombustion gases in such a manner that the same are first dischargedfrom the combustion chamber into a primary heat exchanger, whereuponthey pass for reheating around the combustion chamber in a passageformed between the double walls thereof, and thereafter the gases passthrough a secondary heat exchanger and are then expelled in cooled stateto the outside, normally by suction of a suitable fan.

' The novel features which I consider as characteristic for my inventionare set forth in particular in the appended claims. The inventionitself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection withthe accompanying drawings, inwhich:

The figure presents a sectional View, in schematic, of one embodiment ofmy invention.

A low temperature heater is illustrated in the drawing, comprising ahollow heating element made of refractory material and having on itsinterior a combustion chamber a. surrounded by double wallsanddimensioned and equipped in accordance with the type of fuel used,which may be of solid, liquid or gaseous substance. A primary heatexchanger b is located adjacent to the exterior of the combustionchamber a-and is made of a metal of high thermal conductivityandcomprises tubes which are smooth on the inside and provided with finson the outside; said g from the exteriorlof the heating element.

A secondary heat exchanger d, similar to the primary heat exchanger b,is located near the same and comprises tubes having a smooth surface onthe interior and integral fins on the exterior; said tubes are connectedwith one end to the conduit for providing continuous communicationtherewith and are connected with the other end to a waste gas collectore. A fan i is provided adjacent to the waste gas collector e andarranged to provide an induced draught for the entire path of fumes forremoving the combustion gases from the collector for discharge into achimney.

Furthermore, the device comprises a shaft 9 housing the two heatexchangers b and d and adapted to direct over these exchangers a streamof cool air to be heated.

The operation of my device is as follows:

Owing to the reduced pressure provided by the action of the fan I, thegases are forced through the primary heat exchanger b .where their heatis given off, heating the cold air surrounding them. Thereafter, theyarrive in a fairly cool state in the passage 0, adjacent to thecombustion chamber a, and bypassing through the passage they absorb heatdeveloped in the combustion chamber a. After being thus reheated, thegases flow through the tubes of the secondary heat exchanger d, thereingiving off their heat, and are finally discharged through the chimney byfan action. I

Cool air is directed into the device by the duct g and is heated whilepassing over the exterior surface of the tubes of the two heatexchangers which areprovidedwith fins, as already setforth above, forincreasing the exterior surface area and thereby promoting the rate ofheat transmission.

The heat exchange occurs under particular conditions specified below.Only a portion'of the heat developed by combustion is taken along by thegases which transmit it by means of the primary heat exchanger 1) to theair to be heated; the other portion of the heat is absorbed by the wallsof the combustion chamber which transmit it to the gases directedthrough the passage 0 therein, and is finally used to heat the air bymeans of the second heat exchanger d.

It is therefore possible to have a combustion chamber of hightemperature, and to reduce excess air of combustion to a practicallynegligible value resulting in a high degree of efficiency of Combustion.Since on the other hand, the heat of combustion is in fact completelypassed along to the cool air by the heat exchangers, the overallefiiciency of the heater is very high.

The rate of transfer. of heat between the hot gases and the heatexchangers, as well as that between the exchangers and the cold air, isproportional to the product of the surface area of heat transmission andthe difference of temperature levels.

Transfer of heat between the hot gases and the heat exchangers takesplace along the relatively small inner smooth surface of the tubes;hence the difference in temperature should be great. On the other hand,as the transfer of heat between the heat exchangers and the cold airtakes. place along the outer surface of the tubes provided with fins andconsequently relatively large, the difference in temperature maytherefore be small. In view of the high thermal conductivity ooefficientof the metal from which the tubes are I made, it is possible, forpractical purposes, to disregard the difference of temperature betweenthe At the at a low cost by using commercial metals which areinexpensive and easily available.

The. heater may also be used without fan at a lower rate with naturaldraught action.

It will be understood that each of the elements described above, or twoor more together, may also find. a, useful-application in other types ofimprovements, in low temperature heaters, differing from the typesdescribed above.

WhileI have illustrated and described the in.- vention as embodied inlow temperature heaters, I do notintend. to. be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of my invention.

Without further analysis, the foregoing will so fully reveal the gist ofmy invention that others can by applying current knowledge readily adaptit for various applications without omitting features that, from thestandpoint of prior art, fairly constitute. essential characteristics ofthe generic or specific aspects of this invention, and, therefore suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the following claims.

What. I claim as new and desire to secure by Letters Patent is:

1., In a low temperature heater, a heating element having on theinterior a. chamber for fuel combustion and a passage around the sameseparated therefrom by a heat conductive wall surrounding said chamber;and a plurality of exposedheat exchangers each including a tube having asmooth interior surface and carrying fins on the exterior surface forproviding a large surface area, and, each arranged so as to conductgases through its interior and so as to be surrounded by the cool airto. be heated and to heat 4 with one end to said chamber and with itsother end to one end of said passage for receiving combustion gasesdeveloped in said chamber and emanating therefrom at elevatedtemperatures and for conducting them to said passage, and another ofsaid heat exchangers connected to the other end of said passage forconducting gases therefrom, said passage thus connecting said heatexchangers and adapted to conduct gases therebetween and adjacent tosaid heat conductive wall surrounding said chamber for causing, thegases to be reheated.

2. In a low temperature heater for heating air, a heating element havingon the interior a chamvberfor fuel combustion and a passage around thesame separated therefrom by a heat conductive wall surrounding saidchamber, a plurality of heat fins-onthe exterior surfaces for providinglarge,

surface areas and each arranged to conduct gases through its interiorand each surrounded by the cool. air to be heated; one of said heatexchangers connected with one end to said chamber and with its other endto one end of said passage for receiving combustion gases developed insaid chamber and emanating therefrom at elevated temperatures and forconducting them to said passage; another of said heat exchangersconnected to the other end of said passage for conducting gasestherefrom, said passage thus connecting said heat exchan ers and adaptedto conduct gases therebetween and adjacent: to said heat conductive wallsurrounding said chamber for causing the gases to be reheated, and meansarranged to admit the cold air to be heated. and to direct the sametowards the exterior surface of said heat exchangers.

3. In a. low temperature heater for heating air, a heating elementhaving on the interior a chamber for fuel combustion, and a passagearound the same separated therefrom by a heat conductive wall,surrounding said chamber; and a plurality of exposed heat exchangerseach arranged so as to conduct gases through its interior and so as .tobesurrounded by the cool air to be heated and. to heat the same, one ofsaid heat exchangers connected with one end to said chamber and with itsother end to. one end of said passage for receiving combustion gasesdeveloped in said chamber and emanating therefrom at elevatedtemperatures and for conducting them to said passage, and another ofsaid heat. exchangers connected to the other end of said passage forconducting gases therefrom, said passage thus connecting said heatexchangers and adapted to conduct gases therebetween, and adjacenttosaid heat conductive wall surrounding said chamber for causing thegases to be reheated.

4. In a low temperature heater for heating air, a heating element havingon the interior a. chamber for fuel combustion and a passage around thesame separated therefrom by a heat conductive wall surrounding saidchamber, a plurality of heat exchangers each arranged to conduct gasesthrough its interior and each surrounded by the cool air to be heated;one of said heat exchangers connected with one end to said chamber andwith its other" end to one end of said passage for-receiving combustiongases developed in said chamber and emanating therefrom at elevatedtemperatures and for conducting them to said-passage; anotherof saidheat exchangers connected to the; other end of: said passage forconducting gases therefrom, said passage thus connecting said heatexchangers and adapted to conduct gases therebetween and adjacent tosaid heat conductive wall surrounding said chamber for causing the gasesto be reheated; and means arranged to admit the cold air to be heatedand to direct the same towards the exterior surface of said heatexchangers.

PIERRE GEORGES VICARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 0 Number 6 UNITED STATES PATENTS Name Date Evans Apr. 25, 1893Keller Dec. 10, 1940 Nelson Sept. 2, 1941 Gygi July 10, 1945 FOREIGNPATENTS Country Date Switzerland T Sept. 1, 1944

